U.S. patent number 5,556,912 [Application Number 08/361,202] was granted by the patent office on 1996-09-17 for aqueous binder dispersion for physically drying coating compositions and use thereof.
This patent grant is currently assigned to Herberts GmbH. Invention is credited to Thomas Brock, Klaus Wandelmaier.
United States Patent |
5,556,912 |
Brock , et al. |
September 17, 1996 |
Aqueous binder dispersion for physically drying coating
compositions and use thereof
Abstract
Improved aqueous binder dispersions including polyurethanes and
water-based physically drying coating compositions containing these
aqueous dispersions which are particularly suitable for plain and
metallic colored base coats employed for automotive repair lacquer
coatings.
Inventors: |
Brock; Thomas (Hurth,
DE), Wandelmaier; Klaus (Wuppertal, DE) |
Assignee: |
Herberts GmbH (Wuppertal,
DE)
|
Family
ID: |
6505922 |
Appl.
No.: |
08/361,202 |
Filed: |
December 21, 1994 |
Foreign Application Priority Data
|
|
|
|
|
Dec 23, 1993 [DE] |
|
|
43 44 063.0 |
|
Current U.S.
Class: |
524/507; 427/258;
524/539; 524/591; 524/839; 524/840; 525/123; 525/455 |
Current CPC
Class: |
B05D
7/53 (20130101); C08F 290/147 (20130101); C08G
18/675 (20130101); C09D 175/04 (20130101); C09D
175/14 (20130101); C08G 18/675 (20130101); C08G
18/6659 (20130101); C08G 18/675 (20130101); C08G
18/0819 (20130101); C09D 175/04 (20130101); C09D
175/14 (20130101); C08L 75/04 (20130101); C08L
75/04 (20130101) |
Current International
Class: |
B05D
7/00 (20060101); C08G 18/00 (20060101); C08F
290/14 (20060101); C08F 290/00 (20060101); C09D
175/14 (20060101); C08G 18/67 (20060101); C09D
175/04 (20060101); C08J 003/00 (); C08K 003/20 ();
C08L 075/00 (); B05D 001/36 () |
Field of
Search: |
;524/507,539,591,839,840
;525/123,455 ;427/258 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Michl; Paul R.
Assistant Examiner: Niland; Patrick
Attorney, Agent or Firm: Schweitzer Cornman & Gross
Claims
We claim:
1. Aqueous dispersion of a binder suitable for coating compositions
containing a mixture of:
A) 45 to 95 wt. % of one or more polyurethanes, obtained by
free-radical initiated polymerisation of polyurethane macromonomers
containing carboxyl, phosphonic and/or sulphonic acid groups and
lateral vinyl groups, optionally together with terminal vinyl,
hydroxy, urethane, thiourethane and/or urea groups in the presence
of one or more unsaturated monomers copolymerisable with the
polyurethane macromonomer, in the form of an aqueous dispersion
and
B) 5 to 55 wt. % of one or more polyurethane resins containing
ionic groups containing neither urea nor carbonate groups, which
resins have a number average molar mass (M.sub.n) of 10000 to
300000 and an acid value of 5 to 50 in the form of an aqueous
dispersion, obtained by preparing a polyurethane prepolymer
containing OH groups and having an OH value of 5 to 75 and a number
average molar mass (M.sub.n) of 5000 to 50000 by the reaction in an
organic medium of
a) one or more isocyanate-reactive compounds with an acid value of
0 to 10 in the form of
a1) 70 to 100 wt. % of one or more polyester polyols and/or
polyether polyols, in particular polyester diols, polyether diols
with a molecular weight of 500 to 6000, together with
a2) 30 to 0 wt. % of one or more compounds differing from a1) with
at least two isocyanate-reactive groups with a molecular weight of
60 to 400 with
b) one or more reaction products containing free isocyanate groups
prepared from
b1) at least one compound with two isocyanate-reactive groups and
at least one anionic group or group capable of anion formation
and
b2) one or more organic diisocyanates
in a quantity ratio such that the molar ratio of the
isocyanate-reactive groups of b1) to the isocyanate groups of b2)
is 1:1.5 to 1:2.5, wherein the reaction product b) may be produced
in the presence of component a), wherein component b) is used in
such a quantity that the finished polyurethane resins have the
desired acid value and with
c) one or more polyisocyanates with at least two free isocyanate
groups per molecule in a quantity such that the molar ratio of the
OH groups of component a) to the NCO groups of components b) and c)
is 1.01:1 to 3:1,
whereupon, before or after partial or complete neutralisation of
groups which may be converted into ionic groups in the organic
medium or after conversion into the aqueous phase, the prepolymer
obtained from a), b) and c) is subjected to chain extension by
reaction with
d) one or more polyfunctional isocyanates with a free NCO group
functionality of at least 1.8, in proportions such that the
finished polyurethane resins have the desired number average molar
mass, wherein the wt. % of the components A) and B) each relate to
the resin solids content.
2. Aqueous coating composition containing
8 to 20 wt. %, related to the weight of resin solids, of a
dispersion according to claim 1,
50 to 90 wt. % water,
0 to 20 wt. % of one or more organic solvents,
0.1 to 20 wt. % of one or more effect pigments and/or chromophoric
pigments and/or extenders,
neutralising agent to achieve a degree of neutralisation of the
neutralisable groups of the binder of 40-120%, optionally together
with customary additives and auxiliary substances.
3. Process for the production of multicoat lacquer coatings by
applying a base coat of an aqueous coating composition onto an
optionally pretreated substrate and subsequent application of a
transparent topcoat lacquer, characterised in that a coating
composition according to claim 2 is used as the aqueous coating
composition for the base coat.
4. Process according to claim 3, characterised in that the aqueous
base coat lacquer coat is dried at temperatures of 15 to 60.degree.
C.
5. Process according to claim 3, characterised in that the aqueous
base lacquer coat is applied wet-on-wet with the transparent
topcoat lacquer coat, whereupon the two coats of lacquer are dried
together.
Description
BACKGROUND OF THE INVENTION
This invention relates to aqueous binder dispersions and to
water-based physically drying coating compositions containing these
dispersions which are in particular suitable for plain and metallic
coloured base coats.
There is an industrial and commercial requirement for physically
drying coating compositions which are in particular suitable for
repair lacquer coatings of various substrates, such as metal
articles, in particular in the automotive sector or for the lacquer
coating of machinery. Coating compositions are required for such
purposes which dry or cure at room temperature or with slight
heating, for example to temperatures of up to 60.degree. C.
OBJECT OF THE INVENTION
Such physically drying coating compositions, which are for example
suitable for automotive repair lacquer coatings, are known, for
example from DE-A-41 15 015 and DE-A-41 15 042. However, in
multicoat structures these known coating compositions based on
polyurethane binders still exhibit disadvantages in comparison with
conventional solvent-borne base lacquers. In particular, the
hardness of the overall structure is inadequate.
SUMMARY AND DETAILED DESCRIPTION OF THE INVENTION
DE-A-41 22 265 also describes polyurethane dispersions which, after
conversion into the aqueous phase, are inter alia suitable for the
production of metallic and plain base lacquers. The polyurethane
dispersions are produced by free-radical initiated polymerisation
of polyurethane macromonomers with lateral vinyl groups. The
principal disadvantage of these coating compositions is inadequate
water resistance, which in particular becomes evident under
automotive repair lacquer coating conditions.
DE-A-39 36 794 describes polyurethaneureas and the use thereof as
binders in aqueous metallic base lacquers. The binder contains at
least 200 milliequivalents of chemically incorporated carbonate
groups per 100 g of solids. However, in comparison with
solvent-based base lacquers, base coats on this basis exhibit
deficient hardness of the overall structure, in particular when
overcoated with conventional clear lacquers.
The as yet unpublished German patent application P 43 23 896
describes further aqueous polyurethane dispersions which are
resistant to hydrolysis and stable in storage and are obtained by
chain extension of a polyurethane prepolymer with polyisocyanate.
They may be used in multicoat lacquer coatings for topcoat lacquer
and base coats. Unsatisfactory water resistance is achieved with
the described polyurethane dispersions under the special conditions
of automotive repair lacquer coating or similar applications
requiring low curing temperatures.
The object of the invention is to provide binders for water-based
physically drying coating compositions which, as the base lacquer
in a multicoat structure, achieve the characteristics of
conventional base lacquers, in particular with regard to hardness
and water resistance.
This object is achieved by an aqueous dispersion of a binder
suitable for coating compositions, which dispersion contains a
mixture of
A) 45 to 95 wt. % of one or more polyurethanes, obtainable by
free-radical initiated polymerisation of polyurethane macromonomers
containing carboxyl, phosphonic and/or sulphonic acid groups and
lateral vinyl groups, optionally together with terminal vinyl,
hydroxy, urethane, thiourethane and/or urea groups in the presence
of one or more unsaturated monomers copolymerisable with the
polyurethane macromonomer, in the form of an aqueous dispersion
and
B) 5 to 55 wt. % of one or more polyurethane resins containing
ionic groups containing neither urea nor carbonate groups, which
resins have a number average molar mass (M.sub.n) of 10000 to
300000 and an acid value of 5 to 50 in the form of an aqueous
dispersion, obtainable by preparing a polyurethane prepolymer
containing OH groups and having an OH value of 5 to 75 and a number
average molar mass (M.sub.n) of 5000 to 50000 by the reaction in an
organic medium of
a) one or more isocyanate-reactive compounds with an acid value of
0 to 10 in the form of
a1) 70 to 100 wt. % of one or more polyester polyols and/or
polyether polyols, in particular polyester diols and/or polyether
diols with a molecular weight of 500 to 6000, together with
a2) 30 to 0 wt. % of one or more compounds differing from al) with
at least two isocyanate-reactive groups with a molecular weight of
60 to 400 with
b) one or more reaction products containing free isocyanate groups
prepared from
b3) at least one compound with two isocyanate-reactive groups and
at least one anionic group or group capable of anion formation
and
b2) one or more organic diisocyanates
in a quantity ratio such that the molar ratio of the
isocyanate-reactive groups of b1) to the isocyanate groups of b2)
is 1:1.5 to 1:2.5, wherein the reaction product b) may be produced
in the presence of component a), wherein component b) is used in
such a quantity that the finished polyurethane resins have the
desired acid value and with
c) one or more polyisocyanates with at least two free isocyanate
groups per molecule in a quantity such that the molar ratio of the
OH groups of component a) to the NCO groups of components b) and c)
is 1.01:1 to 3:1, whereupon, before or after partial or complete
neutralisation of groups which may be converted into ionic groups
in the organic medium or after conversion into the aqueous phase,
the prepolymer obtained from a), b) and c) is subjected to chain
extension by reaction with
d) one or more polyfunctional isocyanates with a free NCO group
functionality of at least 1.8, in proportions such that the
finished polyurethane resins have the desired number average molar
mass, wherein the wt. % of the components A) and B) each relate to
the resin solids content.
The present invention also provides aqueous coating compositions
containing:
8 to 20 wt. %, related to resin solids, of one or more dispersions
as described above,
50 to 90 wt. % water,
0 to 20 wt. % of one or more organic solvents,
0.1 to 20 wt. % of one or more effect pigments and/or chromophoric
pigments and/or extenders,
neutralising agent to achieve a degree of neutralisation of the
neutralisable groups of the binder of 40-120%, optionally together
with customary additives and auxiliary substances.
Component A) of the binder used according to the invention
comprises one or more polyurethanes produced by free-radical
initiated polymerisation of polyurethane macromonomers containing
carboxyl, phosphonic and/or sulphonic acid groups and lateral vinyl
groups, optionally together with terminal vinyl groups, hydroxyl-,
urethane, thiourethane and/or urea groups in an unsaturated monomer
copolymerisable with the polyurethane macromonomer and acting as a
solvent, optionally in the presence of further different
copolymerisable unsaturated monomers or by free-radical initiated
polymerisation of the polyurethane macromonomers in a mixture of
water and an organic solvent inert towards isocyanate groups, in
the presence of unsaturated monomers copolymerisable with the
polyurethane macromonomers, and optionally with elimination of the
organic solvent by distillation before or after free-radical
polymerisation. The polyurethanes are present in the form of
aqueous dispersions.
The polyurethane dispersions (component A) may be produced in
various manners. One route consists in producing a polyaddition
product (polyurethane macromonomer) by polyaddition of polyhydroxy
compounds from the group comprising polyhydroxy polyethers,
polyhydroxy polyesters or polyhydroxy polycarbonates, and also
polyhydroxycarboxylic acids, dihydroxyphosphonic acids and/or
polyhydroxysulphonic acids, together with polyisocyanates and a
monomer containing at least two hydroxy and at least one vinyl
group. The quantity ratios of the reactants, in particular of the
polyisocyanate, may here be selected such that a macromonomer with
terminal hydroxyl groups is produced. After conversion into an
aqueous dispersion, this macromonomer, which also contains carboxyl
or sulphonic acid groups and lateral vinyl groups, is polymerised
via the vinyl groups with c6polymerisable unsaturated monomers and
free-radical initiators to yield the polyurethane dispersion,
wherein in this case the polyurethane still bears hydroxyl
groups.
In contrast with the above-described variant, a second route
consists in selecting the quantity ratio of polyisocyanate such
that a macromonomer with terminal isocyanate groups is
produced.
This macromonomer additionally contains carboxyl, phosphonic acid
and/or sulphonic acid groups, together with lateral vinyl groups.
The free isocyanate groups of this macromonomer are then reacted
with primary or secondary amines or thioalcohols to yield urea,
urethane or thiourethane groups. The macromonomer modified in this
manner is then also polymerised via the vinyl groups with
copolymerisable unsaturated monomers and free-radical
initiators.
A third route consists, as in the second process variant, in
producing a polyaddition product by reaction of polyhydroxy
compounds from the group comprising polyhydroxy polyethers,
polyhydroxy polyesters or polyhydroxy polycarbonates, and also
polyhydroxycarboxylic acids, dihydroxyphosphonic acids and/or
polyhydroxysulphonic acids, and polyisocyanates and additionally at
least one monomer containing at least one vinyl group and at least
two hydroxy groups. In this case too, an excess of polyisocyanate
is used, such that the resultant macromonomer has lateral vinyl
groups together with carboxyl, phosphonic acid and/or sulphonic
acid groups together with terminal isocyanate groups. This
macromonomer is then reacted with at least one monomer, which in
addition to a vinyl group also contains one further group which
reacts with isocyanate groups, such as for example a hydroxyl,
amino or mercapto group. These monomers may be used alone, but it
is also possible to use these monomers mixed with primary or
secondary amines, alcohols or thioalcohols. In this manner, a
macromonomer is obtained which contains lateral vinyl groups
together with terminal vinyl groups. This macromonomer is then also
polymerised in a final stage via the vinyl groups with
copolymerisable unsaturated monomers and free-radical
initiators.
A fourth process variant consists in the monomer, which bears the
carboxyl, phosphonic acid and/or sulphonic acid group, first being
incorporated into the previously formed macromonomer. In this
process variant, a polyaddition product is first formed from
polyhydroxy polyethers, polyhydroxy polyesters or
polyhydroxycarbonates, polyisocyanates and monomers, which contain
both at least one vinyl group and at least two hydroxyl groups.
Here too, a molar excess of polyisocyanate is used, such that the
resultant macromonomer contains terminal isocyanate groups. In
addition, this macromonomer then also contains lateral vinyl
groups.
The intermediate product formed may moreover also be chain extended
by the isocyanate groups of this polyaddition product being
reacted, for example, with diaminocarboxylic acids or
diaminosulphonic acids. Here too, the vinyl groups are finally
polymerised with copolymerisable unsaturated monomers using
free-radical initiation.
Examples of the polyhydroxyl polyethers for production of the
polyurethane macromonomers are compounds of the general formula
in which
R is hydrogen or a lower alkyl residue (for example with
C.sub.1-6 or C.sub.1-4, optionally with various substituents,
n is a number from 2 to 6 and
m is a number from 10 to 120.
Specific examples are poly(oxytetramethylene) glycols,
poly(oxyethylene) glycols and poly(oxypropylene) glycols. The
preferred polyhydroxy polyethers are poly(oxypropylene) glycols
with a molecular weight in the range from 400 to 5000.
Examples of usable polyhydroxy polyesters are those produced by
esterification of organic polycarboxylic acids or the anhydrides
thereof with organic polyols. The polycarboxylic acids and the
polyols may, for example, be aliphatic or aromatic polycarboxylic
acids and polyols.
The polyols used for production include, for example, alkylene
glycols such as ethylene glycol, butylene glycol, neopentyl glycol
and other glycols such as diethylolcyclohexane, together with
trishydroxyalkylalkanes, such as for example trimethylolpropane and
tetrakishydroxylalkylalkanes, such as for example
pentaerythritol.
The acid component of the polyester preferably principally consists
of low molecular weight polycarboxylic acids, for example
dicarboxylic acids, or the anhydrides thereof with 2 to 18 carbon
atoms per molecule. Suitable acids are, for example, phthalic acid,
isophthalic acid, terephthalic acid, tetrahydrophthalic acid,
hexahydrophthalic acid, succinic acid, adipic acid, azelaic acid,
sebacic acid, maleic acid, glutaric acid,
hexachloroneptanedicarboxylic acid, tetrachlorophthalic acid,
trimellitic acid and pyromellitic acid. It is also possible to use
the anhydrides of these acids, where they exist, instead of the
acids. Dimeric and trimeric fatty acids may also, for example, be
used as polycarboxylic acids.
Further starting compounds which may be considered are
polycarbonate polyols or polycarbonate diols which are, for
example, of the general formula ##STR1## in which the residues R'
which may be identical or different, mean an alkylene residue.
These OH-functional polycarbonates may be produced by reacting
polyols such as 1,3-propanediol, 1,6-butanediol, diethylene glycol,
triethylene glycol, 1,4-bishydroxymethylcyclohexane,
2,2-(bis(4-hydroxycyclohexyl)propane, neopentyl glycol,
trimethylolpropane, pentaerythritol, with dicarbonates, such as
dimethyl, diethyl or diphenyl carbonate, or with phosgene. Mixtures
of such polyols may also be used.
It is of particular significance to the polyurethane dispersions
for the macromonomers which give rise to these dispersions to
contain lateral vinyl groups, optionally together with terminal
vinyl groups. The term "terminal vinyl groups" is intended to
denote vinyl groups attached to the beginning or end of the polymer
chain, while lateral vinyl groups are those not attached to the
beginning or end of the polymer chain but instead incorporated
between the beginning and end.
The lateral vinyl groups in the polyurethane dispersions are
obtained by incorporating monomers containing at least two hydroxyl
groups and at least one vinyl group into the macromonomer. Examples
are trimethylolpropane (TMP) derivatives such as for example
TMP-monoallyl ether (2-propenyloxy-2-hydroxymethylpropanol),
TMP-mono(meth)acrylate(2-(meth)acryloyloxy-2-hydroxmethylpropanol);
glycerol mono(meth)acrylate; addition products of
.alpha.,.beta.-unsaturated carboxylic acids, such as (meth)acrylic
acid, onto diepoxides, for example bisphenol A diglycidyl ethers,
hexanediol diglycidyl ethers; addition products of dicarboxylic
acids, such as for example adipic acid, terephthalic acid or the
like onto (meth)acrylic acid glycidyl esters; monovinyl ethers of
polyols.
The polyurethane macromonomers may be produced using customary
methods known in urethane chemistry. Catalysts may, for example, be
used, such as for example tertiary amines, such as for example
triethylamine, dimethylbenzylamine, diazabicyclooctane, together
with dialkyltin(IV) compounds, such as for example dibutyltin
dilaurate, dibutyltin dichloride, dimethyltin dilaurate. In
particular, the reaction proceeds in the presence of a solvent or
in the presence of a so-called reactive diluent. Solvents which may
be considered are those which may subsequently be eliminated by
distillation, for example methyl ethyl ketone, methyl isobutyl
ketone, acetone, tetrahydrofuran, toluene, xylene. These solvents
may be entirely or partially removed by distillation after
production of the polyurethane macromonomers or after free-radical
polymerisation. Instead of or in addition to these solvents, it is
also possible to use water-dilutable high boiling solvents, for
example N-methylpyrrolidone, which then remain in the dispersion.
Reactive diluents which may be used are, for example,
.alpha.,.beta.-unsaturated monomers as are copolymerised in the
final state with the macromonomers containing vinyl groups. Example
of such monomers, which may also be used as reactive diluents, are
.alpha.,.beta.-unsaturated vinyl monomers such as alkyl acrylates,
alkyl methacrylates and alkyl crotonates with 1 to 20 carbon atoms
in the alkyl residue, di-, tri- and tetraacrylates, -methacrylates
and -crotonates of glycols, tri- and tetrafunctional alcohols,
substituted and unsubstituted acrylamides and methacrylamides,
vinyl ethers, .alpha.,.beta.-unsaturated aldehydes and ketones,
vinyl alkyl ketones with 1 to 20 carbon atoms in the alkyl residue,
vinyl ethers, vinyl esters, diesters of .alpha.,.beta.-unsaturated
dicarboxylic acids, styrene, styrene derivatives, such as for
example .alpha.-methylstyrene.
The resultant macromonomers are then neutralised if the acid groups
of the monomers bearing such groups were not used in neutralised
form from the outset.
Neutralisation proceeds, for example, using aqueous solutions of
alkali hydroxides or amines, for example trimethylamine,
triethylamine, dimethylaniline, diethylaniline, triphenylamine,
dimethylethanolamine, aminomethylpropanol, dimethylisopropanolamine
or ammonia. Neutralisation may also be performed with mixtures of
amines and ammonia.
In order to produce the polyurethane dispersion used as component
A), the resultant macromonomers containing vinyl groups are
converted into an aqueous dispersion by adding water and
polymerised by free-radical initiated polymerisation using methods
which are known per se. Unless already present as so-called
reactive diluents, monomers of the type previously described as
reactive diluents are added during this polymerisation operation
and are then polymerised into the polyurethane.
The resultant polyurethanes have a number average molecular weight
(M.sub.n) of 30000 to 500000, preferably of 50000 to 250000. The
proportion of unsaturated monomers to be polymerised into the
polyurethane macromonomer is preferably greater than or equal to 5
wt. %, particularly preferably greater than or equal to 15 wt. %,
related to the weight of the finished total resin.
The acid values of the polyurethane dispersions of component A) are
in the range from 5 to 80 mg KOH/g, preferably 10 to 40 mg
KOH/g.
Such polyurethane dispersions and the production thereof are, for
example, described in DE-A-41 22 265.
The component a1) used in the production of binder component B)
according to the invention preferably comprises linear polyols with
terminal OH groups. Polyether polyols of the general formula I may,
for example, be used.
where
R.sup.2 =hydrogen or a lower alkyl residue (for example with 1 to 6
or 1 to 4 C atoms), optionally with one or more substituents,
n=2 to 6, preferably 3 to 4 and
m=at least 5, for example 5 to 50.
Examples are poly (oxytetramethylene) glycols, poly(oxyethylene)
glycols and poly(oxypropylene) glycols.
The polyether polyols preferably used are those with a molecular
weight in the range between 500 and 3000, which may be produced
without using ethylene oxide, i.e. in particular exclusively using
propylene oxide or tetrahydrofuran. Their OH value is preferably 40
to 220.
Component al) may also include hydrophilic polyols with one or two
isocyanate-reactive hydrogen atoms, which polyols bear in their
side chain polyether chains containing ethylene oxides, or mixtures
thereof. These bring about improved dispersion of the polyurethanes
in the aqueous phase.
Polyester polyols may moreover or additionally be used as component
al). The polyester polyols may, for example, be produced by
esterification of organic dicarboxylic acids or the anhydrides
thereof with organic polyols. The dicarboxylic acids and the
polyols may be aliphatic or aromatic dicarboxylic acids and
polyols.
The polyols used to produce the polyester polyols are, for example,
diols such as alkylene glycols, for example ethylene glycol,
butylene glycol, neopentyl glycol and other glycols such as
dimethylolcyclohexane. It is also possible additionally to use
small quantities of more highly functional OH components or
mixtures thereof with monofunctional OH components, such as for
example trimethylolpropane, pentaerythritol, glycerol, hexanetriol;
polyethers which are condensation products of glycols with alkylene
oxides; monoethers of such glycols, such as diethylene glycol
monoethyl ether, tripropylene glycol monomethyl ether.
The acid component of the polyester polyol preferably primarily
consists of low molecular weight dicarboxylic acids or the
anhydrides thereof with 2 to 18 carbon atoms per molecule.
Suitable acids are, for example, phthalic acid, isophthalic acid,
terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid,
adipic acid, sebacic acid, fumaric acid, maleic acid, glutaric
acid, succinic acid or itaconic acid. It is also possible to use
the anhydrides of these acids, where they exist, instead of the
acids. It is also possible, in order to obtain branched polyesters,
to add quantities of trifunctional carboxylic acids, such as
trimellitic acid, malic acid, aconitic acid,
bishydroxyethyltaurine, together with dimethylolpropionic acid.
The polyester polyols preferably have a molecular weight of 400 to
6000, an OH value of 20 to 280 and an acid value of less than 3.
Linear polyester polyols are preferably used.
It is also possible to use polyester polyols, preferably diols,
derived from lactones as component al) in the invention. These
products are, for example, obtained by reacting an e-caprolactone
with a diol. Such products are, for example, described in U.S. Pat.
No. 3,169,945.
The polylactone polyols obtained from this reaction are
distinguished by the presence of terminal hydroxyl groups and
polyester repeat units derived from the lactone.
These molecular repeat units may, for example, be of the general
formula ##STR2## in which n is preferably 4 to 6 and the
substituent R.sup.3 is hydrogen, an alkyl residue, a cycloalkyl
residue or an alkoxy residue, wherein no substituent contains more
than 12 carbon atoms and the total number of carbon atoms in the
substituent in the lactone ring does not exceed 12.
The lactone used as starting material may be any desired lactone or
any desired combination of lactones, wherein this lactone may, for
example, contain 6 to 8 carbon atoms and wherein at least two
hydrogen substituents are preferably present on the carbon atom
which is attached to the oxygen group of the ring. The lactone used
as starting material may be represented by the following general
formula III: ##STR3## in which n and R.sup.3 have the meaning
already stated.
The lactones preferred in the invention for the production of the
polyester diols are .epsilon.-caprolactones in which n has a value
of 4. The most preferred lactone is unsubstituted
.epsilon.-caprolactone in which n has the value 4 and all the
R.sup.3 substituents are hydrogen. This lactone is particularly
preferred because it is available in large quantities and produces
coatings with excellent properties. Various other lactones may
moreover also be used individually or combined.
Examples of aliphatic diols suitable for the reaction with the
lactone include ethylene glycol, 1,3-propanediol, 1,4-butanediol,
dimethylolcyclohexane.
Sequenced polydiols prepared from polyethers and polyesters may
also be used.
The diols al) are preferably substantially free of carboxyl groups,
i.e. only very small proportions of unreacted COOH groups are
present. The acid value is preferably less than 10 mg KOH/g, in
general less than 5. These small proportions of optionally ionic
groups or groups which may be converted into ionic groups make no
contribution to stabilisation of the aqueous dispersions.
Mixtures of various diols al) may also be used.
The optionally used low molecular weight compounds a2) are, for
example, low molecular weight alcohols. These are compounds with a
molecular weight of below 400 containing at least difunctional
hydroxyl groups known per se from polyurethane chemistry in the
context of an isocyanate addition reaction. Compounds which may be
considered in the context of the isocyanate addition reaction are
both difunctional compounds and at least trifunctional compounds or
any desired mixtures of such compounds. In particular, it is
preferred to use diols in the reaction.
Examples of such components are low molecular weight polyhydric
alcohols, for example aliphatic alcohols, such as ethylene glycol,
1,2- and 1,3-propanediol, 1,4- and 1,3-butanediol, 1,6-hexanediol,
1,8-octanediol, neopentyl glycol, 1,4-bishydroxymethylcyclohexane,
2-methyl-1,3-propanediol, 2,2,4-trimethyl-l,3-pentanediol,
trimethylolethane, isomeric hexanetriols or pentaerythritol or
mixtures thereof. Such polyol compounds have, in particular, a
molecular weight of less than 400.
The quantity of low molecular weight compound.sub.s a2) may be up
to 30 wt. % related to a). The degree of branching may be
controlled by means of the quantity of more highly functional
polyols. Care must, however, be taken to ensure that crosslinking
is largely avoided.
According to the invention, NCO-terminated compounds are used as
component b), which are obtained by reacting compounds b1) bearing
two isocyanate-reactive groups and at least one anionic group or
group capable of forming anions with aliphatic, cycloaliphatic or
aromatic diisocyanates b2). These are essentially low molecular
weight compounds. In this reaction, the molar ratio of the
non-ionic reactive groups to the isocyanate groups is 1:1.5 to
1:2.5. The ratio is preferably approximately 1:2. These compounds
are then also readily soluble in organic solvents. The reaction
preferably proceeds in liquid form, i.e. the mixture may optionally
contain a proportion of organic non-reactive solvents. The
temperature may optionally be raised somewhat to improve
conversion.
Component b) may be added as a separate component. It is, however,
also possible to produce and further react b) in situ from the
mixture, in the presence of a).
Suitable isocyanate-reactive groups are in particular non-ionic
groups such as hydroxyl groups, thiol groups and primary and
secondary amino groups. Low reactivity, acidic groups capable of
forming anions which may be considered are, for example carboxyl,
phosphonic acid and sulphonic acid groups. Suitable compounds
containing at least two isocyanate-reactive groups and at least one
group capable of forming anions are, for example, dihydroxy acids
and diamino acids. Suitable dihydroxy acids are, for example,
aliphatic and aromatic dihydroxycarboxylic acids, such as
dihydroxypropionic acid, dimethylolpropionic acid, dimethylolacetic
acid, dimethylolbutyric acid, dihydroxysuccinic acid or
dihydroxybenzoic acid. Polyhydroxy acids obtainable by oxidation of
monosaccharides are also suitable, for example gluconic acid,
saccharic acid, mucic acid, glucuronic acid and the like. Examples
of compounds containing amino groups are diaminocarboxylic acids,
such as .alpha.,.delta.-diaminovaleric acid, 3,4-diaminobenzoic
acid, 2,4-diaminotoluene-5-sulphonic acid and 4,4-diaminodiphenyl
ether sulphonic acid. Examples of compounds containing phosphoric
acid groups are 2,2-dimethylolpropanephosphonic acid or
diethanolaminemethanephosphonic acid. The dihydroxycarboxylic acids
are preferred for production of an anionic urethane prepolymer, the
use of dimethylolpropionic acid being particularly preferred.
Any desired organic diisocyanates or mixtures thereof may be
reacted as component b2). Aliphatic or aromatic also sterically
hindered isocyanates or oligomerised isocyanates may, for example,
be used. Examples of suitable diisocyanates are trimethylene
diisocyanate, tetramethylene diisocyanate, pentamethylene
diisocyanate, hexamethylene diisocyanate, propylene diisocyanate,
ethylene diisocyanate, 2,3-dimethylethylene diisocyanate,
1-methyltrimethylene diisocyanate, 1,3-cyclopentylene diisocyanate,
1,4-cyclohexylene diisocyanate, 1,2-cyclohexylene diisocyanate,
1,3-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene
diisocyanate,
1-isocyanato-methyl-5-isocyanato-1,3,3-trimethylcyclohexane,
bis-(4-isocyanatocyclohexyl)methane,
bis-(4-isocyanatophenyl)methane, 4,4-diisocyanatodiphenyl ether,
1,5-dibutylpentamethylene diisocyanate, tetramethylxylylene
diisocyanate and
2,3-bis-(81-isocyanatooctyl)-4-octyl-5-hexylcyclohexane.
The quantity of reaction product b) added to the mixture is such
that the resultant polyesterurethane has an acid value of 5-50,
preferably between 15 and 40. Phosphonic and sulphonic acids are
added in corresponding quantities.
Component b) is, for example, here used in a quantity of
approximately 0.5 to 7 wt. %, preferably approximately 0.8 to
approximately 4.0 wt. % (calculated as carboxyl group) related to
the urethane prepolymer to be produced. If the quantity of carboxyl
groups is less than approximately 0.5%, it is difficult to produce
a stable emulsion. On the other hand, if the quantity exceeds 7 wt.
%, its hydrophilic nature is increased, making the emulsion highly
viscous and reducing the water resistance of the coating.
The aqueous dispersion is stabilised by ionic groups. Ionic and
non-ionic groups may also be used together. Stabilisation using
solely anionic groups is preferred.
Any organic polyisocyanates may be used as component c) for
production of the polyurethane dispersion, in particular also
diisocyanates optionally as a mixture. These are, for example, the
diisocyanates mentioned under b2) or oligomeric isocyanates.
Non-yellowing or sterically hindered isocyanates with 4 to 25,
preferably 6-16 C atoms are preferably used which contain in
d-position relative to the NCO group one or two linear, branched or
cyclic alkyl groups with 1 to 12, preferably 1 to 4 C atoms. The
skeleton may, for example, consist of an aromatic or alicyclic ring
or an aliphatic linear or branched C chain with 1 to 12 C atoms.
Examples of such compounds are isophorone diisocyanate,
4,4'-diphenylpropane diisocyanate, xylylene diisocyanate,
1,1,6,6-tetramethylhexamethylene diisocyanate, p- and
m-tetramethylxylylene diisocyanate and their corresponding
hydrogenated homologues.
It is also possible to react polyisocyanates in which the
isocyanate groups in excess of 2 have been irreversibly
defunctionalised. Compounds to perform defunctionalisation which
may be considered are, for example, low molecular weight, primary
or secondary amines or alcohols.
The quantities of a), b) and c) or of a1), a2), b1) and b2) are
selected such that on reaction a reaction product is produced with
terminal OH groups, i.e. an excess of polyol is used. An OH to NCO
ratio of 1.01 to 3:1 may be used, the range preferably being 1.05
to 2:1, particularly preferably 1.1 to 1.5:1. The reaction product
may be of a branched structure, a linear structure is preferred.
The reaction products have a number average molar mass (M.sub.n) of
5000 to. 50000, preferably greater than 8000 and less than 30000
and an OH value of 5 to 75, preferably greater than 10 and less
than 50. The reaction may proceed in a mixture of all the
components or in stages.
The reaction may proceed without solvents or it may, however, also
be performed in solvents suitable for polyurethane synthesis
familiar to the person skilled in the art. The solvents may remain
in the batch or optionally be eliminated by distillation before
further processing. Further additional solvents may also be added
in order to reduce the viscosity of the polymer solution.
Suitable solvents are those which do not disrupt the reaction of
the isocyanates. These are, for example, aromatic hydrocarbons such
as benzene, toluene, xylene, esters, such as ethyl acetate, butyl
acetate, ethylene glycol monomethyl ether acetate, ethylene glycol
monoethyl ether acetate, methoxypropyl acetate, ethers such as
tetrahydrofuran, dioxane, completely etherified mono- or diglycols
of ethylene glycol or propylene glycol, such as diethylene glycol
or dipropylene glycol dimethyl ether, ketones, such as acetone,
methyl ethyl ketone, halogenated solvents such as methylene
chloride or trichloromonofluoroethane. Solvents which facilitate
dispersion in the aqueous phase are preferred. Solvents which
subsequently have no negative effects in the coating compositions
according to the invention are also preferred.
The OH-functionalised polyurethane prepolymer is chain-extended as
an intermediate product by reaction with further polyisocyanates
d). These are, for example, homogeneously mixed with the
functionalised intermediate product and then reacted optionally by
heating or the reaction promoted by catalysts customary in NCO
chemistry, for example dibutyltin dilaurate (DBTL), amine
derivatives. This may proceed in the organic or aqueous phase
before or after salt formation of the groups which may be converted
into anionic groups, the reaction preferably occurring after
neutralisation in the organic phase.
Suitable polyisocyanates are, for example, customary known lacquer
poly- or diisocyanates, as have been described above for components
b2) and c). They may be on an aliphatic, cycloaliphatic or aromatic
basis. They preferably have a molar mass of less than 1200.
Low molecular weight NCO-terminated prepolymers are also suitable
as polyisocyanates d). These are preferably difunctional. Their
molecular weight is preferably less than 1000.
The groups which may be converted into anionic groups are
neutralised before or after chain extension. Bases are used to this
end, for example ammonia or amines. Suitable amines are primary,
secondary or tertiary amines, for example trialkylamines, such as
trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine
and tri-n-butylamine; N-alkylmorpholines, such as
N-methylmorpholines and N-ethylmorpholine; N-dialkylalkanolamines,
such as N-dimethylethanolamine and N-diethyleneethanolamine;
dialkylamines such as diethylamine, dibutylamine, diisopropylamine;
alkylamines such as ectylamine, hexylamine, isopropylamine,
aminoethanol; mixtures of at least two of these compounds. In
general, between 30% and 100% of the acid groups are converted into
salt groups.
The aqueous dispersion may be produced in a customary manner using
known processes.
The polyurethane dispersion B) has an acid value of 5 to 50
(related to solids), preferably of 15 to 35, particularly
preferably of 15-25. The solids content is preferably 25 to 55 wt.
%. The M.sub.n of the binder is 10000 to 300000, preferably 50000
to 200000, particularly preferably 40000 to 100000. They may
optionally also contain further functional groups, such as for
example OH groups. The resultant dispersions have, for example, an
average particle size of between 10 and 1000 nm, preferably 30 to
500, particularly preferably 30 to 150 nm.
The coating compositions according to the invention contain from 8
to 20 wt. %, related to the complete coating composition, of the
binder containing components A) and B).
The water content of the coating composition according to the
invention is 50 to 90 wt. %, preferably 60 to 85 wt. %. In order to
improve film forming rheology and the metallic effect, the
composition may contain up to 20 wt. %, for example 1 to 20 wt. %,
preferably 6 to 15 wt. %, in each case related to the complete
coating composition, of one or more solvents.
Solvents which may be considered are those as are, for example,
customary in the lacquer sector as lacquer solvents and/or
additives in aqueous coating compositions.
Suitable examples are aromatic solvents, such as xylene, esters,
such as butyl acetate, glycol ethers, such as ethylene glycol
monobutyl ether (2-butoxyethanol), alcohols, such as butanol,
aliphatic hydrocarbons, such as for example mineral spirits.
The coating compositions according to the invention are
particularly suitable for the production of effect, pearlescent or
plain coloured base lacquer coats.
Where metallic pigments are used, 0.3 to 4 wt. % of one or more
metallic pigments related to the complete coating composition are
preferably used. Metallic pigments which may be considered are
customary metal flake or scale pigments, such as metal bronzes, for
example aluminium pigments, such as aluminium bronzes.
Further effect pigments may also be used, for example interference
pigments such as mica coated with titanium dioxide or iron oxide,
coated aluminium or graphite pigments.
In addition to the effect pigments, the coating composition may
also contain further chromophoric pigments. For the production of
plain colour lacquer coats, the compositions contain only
chromophoric pigments. Pigments should be understood to include
customary inorganic or organic extenders, as are familiar to the
person skilled in the art of the lacquer sector.
Examples of inorganic or organic colouring pigments or extenders
are titanium dioxide, micronised titanium dioxide, iron oxide
pigments, carbon black, silicon dioxide, barium sulphate,
micronised mica, talc, azo pigments, phthalocyanine pigments,
quinacridone- or diketopyrrolepyrrole pigments.
The coating compositions according to the invention contain
neutralising agents in order at least partially to neutralise the
neutralisable groups. The degree of neutralisation of the
neutralisable groups is preferably 40 to 120% of the neutralisable
groups and is preferably less than 100%.
Neutralising agents for acid groups which may be considered are
the-bases customary in the lacquer sector, such as the
above-mentioned amines, ammonia or alkanolamines, such as
N,N-dimethylethanolamine.
The coating compositions according to the invention optionally
contain customary additives and auxiliary substances as are used in
the lacquer sector. Such auxiliary substances and additives are
thickeners, rheological additives, antifoaming agents, levelling
agents, inhibitors (for example to inhibit gassing of aluminium
pigments), dispersion and wetting additives.
The additives and auxiliary substances are added in customary
quantities familiar to the person skilled in the art depending upon
the desired effect.
The coating compositions according to the invention may be applied
to various substrates using customary coating processes, for
example by spraying or knife coating. Substrates which may be
considered are metals, plastics, but also wood, glass and other
substrates.
The coating compositions according to the invention are physically
drying, i.e. they require no baking and may, for example, be dried
at temperatures of the order of 15 to 60.degree. C.
After application, the coating compositions according to invention
may be coated with topcoat lacquers, in particular transparent
topcoat lacquers (clear lacquers). Coating with topcoat lacquers
may be performed wet-on-wet after brief flashing off or after
drying of the base lacquer coat produced according to the
invention. The topcoat lacquer coat may be dried together with the
lacquer coat of the coating composition according to the invention.
Topcoat lacquers which may be considered are customary, in
particular transparent, lacquers, as are for example customary in
the automotive sector. These are predominantly solvent-based
lacquers, but water-based topcoat lacquers may also be used.
As mentioned above, the coating compositions according to the
invention may be applied to the most varied substrates. They are
particularly suitable for the production of base coats in multicoat
lacquer structures. A preferred application which may be considered
is lacquer coating motor vehicles or motor vehicle components.
Thanks to their favourable physical drying properties, the coating
compositions according to the invention are particularly suitable
for the production of repair lacquer coatings or as repair lacquer.
They are, however, also suitable for the production of mass
produced baked lacquer coatings.
In contrast with other known aqueous coating compositions used as
base lacquers, very good hardness of the total structure and
excellent water resistance are achieved in multicoat structures
with the coating compositions according to the invention. The
properties achieved in this manner are comparable with those of
solvent-based base lacquers.
The following examples are intended to illustrate the invention.
Parts (pts.) and percentages relate to weight.
PRODUCTION EXAMPLE 1
Polyurethane dispersion A
249.8 g of a polyester produced from neopentyl glycol,
1,6-hexanediol, isophthalic acid and adipic acid with an hydroxyl
value of 37 and an acid value of less than 3 are dissolved together
with 24.7 g of dimethylolpropionic acid and 9.3 g of 1,4-butanediol
in 150 g of acetone while being refluxed. 0.1 g of
2,6-di-tert.-butyl-4-methylphenol and 16.6 g of glycerol
monomethacrylate are then added and homogenised. After adding 134.2
g of tetramethylxylylene diisocyanate, the mixture is stirred at
refluxing temperature until the isocyanate content is 1.08 wt. %,
related to the total weight of the starting materials.
15.5 g of diethanolamine are then quickly added to the resultant
prepolymer solution and homogenised for 30 minutes. After addition
of 13.1 g of triethylamine, 1108 g of water at a temperature of
80.degree. C. are vigorously stirred into the polymer solution. The
acetone solvent is then separated from the resultant dispersion by
vacuum distillation. After adding 51.1 g of methyl methacrylate,
the temperature is raised to 80.degree. C. and the mixture stirred
for a further 30 minutes. 10 vol. % of an ammonium persulphate
solution consisting of 0.8 g of ammonium persulphate and 50 g of
water are then added at 80.degree. C. The remaining amount of the
ammonium persulphate solution is metered in over a period of 30
minutes. The temperature is maintained at 78.degree. to 80.degree.
C. for a further two hours.
After cooling to room temperature, the dispersion is adjusted to a
solids content of 30% and filtered through a 5 mm filter. The
resultant dispersion has a pH value of 7.46.
PRODUCTION EXAMPLE 2
polymethane dispersion B)
582 g of a customary commercial polyester (M.sub.n =1000, OH
value=106), 28.7 g of dimethylolpropionic acid (DMPA) and 124 g of
N-methylpyrrolidone (NMP) are mixed and dissolved at 80.degree. C.
The mixture is then cooled to 50.degree. C. 139 g of isophorone
diisocyanate (IPDI) are added to the mixture, the temperature
raised to 80.degree. C. and 125 g of NMP added. The mixture is
reacted to an NCO value of <0.1%.
33.2 g of dimethylisopropanolamine solution (50% in water) are
added to the reaction product at 80.degree. C. and stirred in for
10 minutes. 1174 g of completely deionised water are slowly added
at 80.degree. C. and thoroughly mixed in. The temperature may fall
here to 50.degree. C. 34.5 g of IPDI are added at 50.degree. C. to
the resultant aqueous dispersion within 10 minutes and the mixture
then heated to 80.degree. C.
A finely divided aqueous, stable dispersion is obtained.
Solids weight: 36% (determined after 30 minutes at 150.degree. C.
in circulating air oven)
Acid value: 17.4 mg KOH/g (solids)
MEQ-amine: 18.4 (milliequivalents per 100 g solids)
MEQ=milliequivalent.
PRODUCTION EXAMPLE 3
Production of metallic aqueous base lacquers
Aqueous metallic base lacquers are produced from dispersions A and
B produced as above together with the following constituents:
23.6 pts. of dispersion A +11.8 pts. of dispersion B)
46.1* pts. of water
7.2 pts. of n-butanol
4.0 pts. of ethylene glycol monobutyl ether
0.5 pts. of N-methylpyrrolidone
0.3 pts. of a customary corrosion inhibitor to prevent aluminium
gassing
2.1 pts. of a customary commercial thickener
0.2 pts. of N,N-dimethyleneethanolamine
4.1 pts. of a customary aluminium paste (60% Al)
The resultant metallic base lacquers have a viscosity of
approximately 30 seconds (DIN cup, 4 mm nozzle, 23.degree. C.) and
are diluted with approximately 10% water to achieve a spraying
viscosity of approximately 20 seconds. Lacquer coatings are
produced with the dispersions as follows:
Lacquer coating tests:
Lacquer coating structure of the examined metal sheets:
Bright polished bodywork sheet metal
Customary single component polyvinylbutyral primer
Customary two component PU filler
Water base lacquer
Customary two component PU clear lacquer, medium solid grade,
solids content 47%.
Aqueous adhesion primers and fillers may, however, also be
used.
Application and drying of topcoat lacquer coat (base lacquer and
clear lacquer):
Spray application of aqueous base lacquer
30 min pre-drying at room temperature
Spray application of clear lacquer
10 min flashing off at room temperature
30 min drying at 60.degree. C.
Definitions:
pts.=parts by weight
PU=polyurethane
PRODUCTION EXAMPLE 4
Production of plain aqueous base lacquers
Aqueous plain base lacquers are produced from dispersions A and B
produced as above together with the following constituents:
23.6 pts. of dispersion A) and
11.8 pts. of dispersion B)
21.1* pts. of water
12.1 pts. of ethylene glycol monobutyl ether
1.3 pts. of a customary commercial thickener
0.14 pts. of N,N-dimethylethanolamine
22.1 pts. of a customary commercial titanium oxide pigment
0.5 pts. of a customary commercial copper phthalocyanine
pigment
0.16 pts. of a customary commercial defoamer
8.1 pts. of a customary commercial PU grinding auxiliary (solids
content 30%)
* in each case, dispersions with a solids content of approximately
40%; if the solids content is low, the quantities of the dispersion
and water are accordingly corrected such that usable coating
compositions with the same solids content are produced.
The resultant plain base lacquers have a viscosity of approximately
40 to 50 seconds (DIN cup, 4 mm nozzle, 23.degree. C.) and are
diluted with approximately 10 to 15% water to achieve a spraying
viscosity of approximately 20 seconds.
Lacquer coatings are produced in a similar manner to production
example 3 using the plain base lacquers.
By way of comparison, a customary commercial solvent-borne base
lacquer based on acrylate/cellulose acetobutyrate is applied in a
lacquer coating structure corresponding to the described
structure.
The properties of the resultant lacquer coatings are shown in the
following table:
______________________________________ Aqueous base Scratch
resistance.sup.1) Hardness.sup.2) lacquers based on: metallic plain
white plain white ______________________________________ Dispersion
A 1 2 16 .mu.m Dispersion B 1-2 2 18 .mu.m Dispersion A and 1-2 2
18 .mu.m Solvent-borne 1-2 2 15 .mu.m base lacquer
______________________________________ Aqueous base Water
resistance.sup.1) Metallic effect.sup.2) lacquers based on:
metallic plain white (flip flop)
______________________________________ Dispersion A 2-3 3 1-2
Dispersion B 2-3 3 3 Dispersion A and 1-2 2 1-2 Solvent-borne 1-2 2
1-2 base lacquer ______________________________________ .sup.1) 1
very good 2 good 3 usable under certain circumstances 4 unusable
.sup.2) Vickers microindentation hardness at 250 mN (HV 100 tester
from Fischer, Sindelfingen)
* * * * *